Analytical Modelling and Optimization of DC-Link Voltage Harmonic Spectra of Full-Bridge Modular Multilevel Converters for Buck and Boost Operation

This paper develops a new analytical solution to the harmonic spectrum of the Full-Bridge Modular Multilevel Converter (FBMMC) dc-side based on phase-shifted carrier pulse width modulation and considering varying dc-link voltage operation. The harmonic distribution of the FBMMC dc-side voltage is analyzed through using double Fourier series analysis. Through the analysis, proper selection of the modulation indexes, carrier displacement angle, and the number of SMs can ensure a significant reduction in the dc-link switching-ripple voltage. Thus, the related filter can be removed or significantly reduced. The developed model is validated through simulation tests of a Grid-Tied FBMMC with a front-end three-phase diode rectifier without passive components in the dc-link,